Aqueous emulsion polymerization systems are well known for the production of many types of polymers, for example, the preparation of homopolymers and copolymers of vinyl acetate. Commercial production of aqueous emulsion polymers results in products which contain varying amounts of unreacted monomers, for example, residual vinyl acetate, since it is not currently technically feasible to carry these polymerization reactions to 100 percent completion. It is thus desirable to minimize the amount of residual monomers in commercial products (e.g., latices) for several reasons from environmental, regulatory and/or economic points of view.
In U.S. Pat. No. 4,529,753, hereafter the '753 patent, there is described a process for minimizing residual monomer in an aqueous polymeric emulsion. The process involves a simultaneous two-step procedure. The emulsion is subjected to a steam stripping operation with the simultaneous introduction of a free radical generating agent until the residual monomer content is not more than 0.05 percent by weight based on the emulsion.
The present invention provides an improved process over such prior art whereby the residual monomer content can be lowered even further in commercially acceptable batch processing times.